I can’t take credit for this one; that goes to Ben Lindsey. But since the answer I needed was buried in a comment, I thought I’d give it a little more googleability.

RubyMine needs to load special test formatters for its built-in RSpec and Cucumber runners to work. You can easily configure it to talk to a Spork server when running tests, but you’ll get a LoadError (“no such file to load — teamcity/spec/runner/formatter/teamcity/formatter”) with a vanilla Spork setup because the server won’t be able to find the RubyMine formatter libraries.

The solution is to add the requisite paths in the Spork prefork block. Here’s mine: